Process for producing castings from an iron alloy containing silicon



3,318,691 PROCESS FOR PRODUCING CASTINGS FROM AN IRON ALLOY CONTAINING SILICON Rudolf Jellinghaus, Schlachthofstrasse 33, Kamen, Westphalia, Germany No Drawing. Filed July 6, 1965, Ser. No. 469,911 4 Claims. (Cl. 75--129) The present application is a continuation-in-part of application Ser. No. 294,246, filed July 11, 1963, and now abandoned, which is a continuation-in-part of application Ser. No. 55,147, filed Sept. 12, 1960, and now abandoned.

The invention relates to the preparation of ferro-silicon alloys which add free cutting and ease of machining, to the wear and corrosion resistance which are conventionally provided by such alloys. Specifically, it concerns the addition of silicon and calcium-silicon to a steel melt substantially devoid of alloying additives to yield a ferrosilicon alloy which enjoys the highly desirable wear and corrosion resistance of such alloys while avoiding the limited machinability or working characteristics which has previously characterized these alloys.

Ferro-silicon alloys and the use of calcium-silicon as a metallurgical scavenging agent have been previously known. In the case of ferro-silicon alloys, such alloys have yielded outstanding wear and corrosion resistance, but have resisted machining, cutting and working. In addition, calcium-silicon has been employed as a scavenging agent in the removal of oxygen or nitrogen in the form of slag. However, the latter technique has not yielded a machinable alloy which also possesses the corrosion and wear resistance of the inventive materials.

It is the object of the present invention to provide ma-- chinable, wear and corrosion resistant steel alloys having silicon contents in excess of 5% by weight, and preferably in the range of to by weight.

The foregoing object is achieved by means of the addition of a combination of silicon and calcium-silicon, in a quantity adequate to yield a silicon content of between 5 to 20% by weight in the ultimate alloy, to molten steel which is substantially devoid of alloying additives and which is prepared from a batch containing at least 30% by weight of scrap steel. In this regard, the remainder of the batch may also comprise steel scrap or conventional steel yielding ingredients, and trace quantities of alloying additives, e.g. aluminum, chromium, etc., may be present but not in such quantities as to appreciably affect the properties of the ultimate alloy.

More precisely, to achieve this result according to the invention, based upon the total quantity of ingredients employed in preparing the inventive alloys, 1 to 3% by weight of calcium-silicon is added to the silicon in the ladle into which the melt is tapped from a cupola furnace. The combination of calcium-silicon and silicon is well mixed with the melt poured into the ladle by stirring for approximately 15 minutes. Then the resultant melt is poured into ingots or pigs, which are then melted in a crucible furnace, preferably with the addition of recycled material having the same silicon content, and recast at a suitable casting temperature, for example, approximately 1250 C.

It should be noted that calcium-silicon compositions normally employed as deoxidizing agents in metallurgical processes such as the preparation of rust resistant steel, are suitable and preferred for the practices of the present invention. Such compositions normally possess a calcium content in the range of to 40% by Weight, and preferably to by weight. It should also be noted that the conventional scavenging function of these calcium-silicon compositions is not realized in the present invention since their addition to the melt does not result in slag United States Patent 0 3,318,691 Patented May 9, 1967 formation, although some ash may be formed, which is preferably removed before the pouring out of the melt.

The silicon is preferably added in the: form of grains or nodules. While silicon nodules having a diameter as large as one inch may be utilized, finer materials, e.g. having a diameter of less than 0.5 inch, are preferred. The calcium silicon is added preferably in a grain size of up to 0.15 inch.

A preferred practice of the present invention is demonstrated by the following example:

Example Fifteen (15 percent by weight of silicon particles, based upon the total quantity of ingredients employed, having an average diameter of 0.25 inch, and 2% by weight of calcium silicon (calcium content 35% by weight), based upon the total quantity of ingredients employed, were introduced into a ladle and then 83% by weight of molten steel being substantially devoid of alloying additives and prepared from a batch comprised of equal parts of steel scrap and virgin steel pigs were poured into this ladle while the melt was maintained at a temperature of 1600" C. The melt was then thoroughly stirred for about 15 minutes, cooled to 1400 C., and cast in the form of pigs. In spite of the thorough stirring, there was not an even distribution and solution of the calcium silicon and of the silicon grains in the body of the pigs. Therefore, to ob tain the necessary homogeneous state, the pigs were then remelted at 1500 C. in a crucible furnace, cooled to 1250 C., and recast in the form of pigs. In this remelting procedure, preferably recycled material of the same silicon content, produced in a foregoing melting process, was added in amounts of between 25 to referring to the material coming from the ladle, the amount of recycled material depending upon the purposes for which the final alloy shall be used. The resultant alloy possessed a silicon content of 15%, a carbon content of approximately 0.7%, and a sulfur content of 0.008%.

The above alloy was machined with a planing tool formed from Widia type H 1 steel and ground without difficulty with a surface grinder. In chip removal machining, cutting rates of up to 50 meters per minute were attained and the alloy possessed a hardness of 526 kgs./ mm. and an impact resistance of 0.19 kgm./cm.

In boiling 50% solutions of nitric and sulfuric acid, the alloy demonstrated a first day resistance to corrosion of 2800 days/mm. and 370 days/mm. respectively, and a second to fifth day resistance of 25,000 days/mm. and 3700 days/mm, respectively.

It should be noted that the alloys prepared by the inven tive methods also exhibit highly desirable resistance to crushing and sudden temperature change, and the inventive methods permit cyclic operation Without burning. Of paramount importance, the inventive methods provide Wear and corrosion resistant ferro-silicon alloys which possess highly desirable machining, cutting and working characteristics not previously realized in such alloys.

What I claim is:

1. A method for the preparation of free cutting, machinable ferro-silicon alloys comprising melting in a cupola furnace a steel yielding batch containing at least 30% by weight of steel scrap, and substantially devoid of alloying additives, maintaining said molten batch at a temperature of at least 1600" C., tapping off said molten batch into a ladle at substantially the same temperature into which ladle between 1 to 3% by weight referred to the final alloy of calcium silicon and 5 to 20% by Weight of silicon referred to the final alloy are contained, dispersing said silicon and said calcium silicon throughout, casting said molten batch and cooling said batch until solidification is obtained, thereafter, re-melting in a crucible furnace and re-casting the resultant alloy at a temperature of about 1250 C. in the form of pigs.

2. A method as claimed by claim 1 in which between to by weight of said silicon and said calcium silicon referred to the batch is added to said molten batch.

3. A method as claimed by claim 1 wherein the silicon is added in pieces in the form of grains or nodules of a diameter of between 0.5 inch and 1.0 inch.

4. A method for the preparation of free cutting, machinable, ferro-silicion alloys comprising melting in a cupola furnace a steel batch containing 50% by weight of steel scrap, and substantially devoid of alloying additives, maintaining said batch at a temperature of 1600 C., adding to said batch 15% by Weight of silicon granules having a diameter of no more than one inch and 1 to 3% by weight of calcium silicon containing between to by weight of calcium, dispersing said silicon and calcium silicon throughout said batch, reducing the temperature of said batch to 1400 C., casting said batch and cooling said batch until solidification of the resultant alloy is achieved, thereafter, re-melting the resultant alloy in a crucible furnace at 1500 C., cooling to 1250 C. and casting in the form of pigs, and cooling to solidification.

References Cited by the Examiner UNITED STATES PATENTS 581,943 5/1897 Saniter 61 1,444,891 2/1923 Walter 75129 1,494,393 5/1924 Walter 75-129 1,560,885 11/1925 Walter 75-129 1,751,185 3/1930 Wust 75-43 1,949,529 3/1934 Browne 7553 2,144,200 1/1939 Rohn et a1. 75-129 2,266,123 12/1941 Kinzel 75129 2,662,819 12/1953 Hofger et a1. 75129 2,715,064 8/1955 Burns 7543 OTHER REFERENCES Greiner et al., Alloys of Iron and Silicon, Monograph, McGraw-Hill, 1933, pages 300, 301.

Journal of the Iron and Steel Institute, Volume CVII, 1923, page 733 (British).

Lewis Property of Free Machining, Iron and Steel, March 1958, page 88.

HYLAND BIZOT, Primary Examin'er.

DAVID L. RECK, Examiner.

H. W. TARRING, Assistant Examiner. 

1. A METHOD FOR THE PREPARATION OF FREE CUTTING, MACHINABLE FERRO-SILICON ALLOYS COMPRISING MELTING IN A CUPOLA FURNACE A STEEL YILDING BATCH CONTAINING AT LEAST 30% BY WEIGHT OF STEEL SCRAP, AND SUBSTANTIALLY DEVOID OF ALLOYING ADDITIVES, MAINTAINING SAID MOLTEN BATCH AT A TEMPERATURE OF AT LEAST 1600*C., TAPPING OFF SAID MOLTEN BATCH INTO A LADLE AT SUBSTANTIALLY THE SAME TEMPERATURE INTO WHICH LADLE BETWEEN 1 TO 3% BY WEIGHT REFERRED TO THE FINAL ALLOY OF CALCIUM SILICON AND 5 TO 20% BY WEIGHT OF SILICON REFERRED TO THE FINAL ALLOY ARE CONTAINED, DISPERSING SAID SILICON AND SAID CALCIUM SILICON THROUGHOUT, CASTING SAID MOLTEN BATCH AND COOLING SAID BATCH UNTIL SOLIDIFICATION IS OBTAINED, THEREAFTER, RE-MELTING IN A CRUCIBLE FURNACE AND RE-CASTING THE RESULTANT ALLOY AT A TEMPERATURE OF ABOUT 1250*C. IN THE FORM OF PIGS. 